Pneumatic tires for automobiles these days are required to have fuel economy (rolling resistance properties) as well as a wide variety of properties including abrasion resistance and wet-skid performance in the tread portion. Various methods have been devised to improve these properties. Especially, the recent strong demand for better fuel economy has led to a trend to use silica as reinforcing filler in rubber compositions for tires. However, silica has hydrophilic silanol groups on the surface and thus has a lower affinity for rubber than carbon black. Accordingly, its use often results in poor abrasion resistance and mechanical strength.
The use of a silane coupling agent or highly reinforcing fine particle silica may be considered to solve the above problems. Fine particle silica, however, is generally very difficult to disperse in rubber compositions and therefore cannot be dispersed well but leaves agglomerates, which makes it impossible to improve abrasion resistance and mechanical strength so much, or rather may deteriorate these properties.
Patent Literature 1, for example, discloses a rubber composition for treads which contains spherical fine particles of amorphous silica as filler and which has improved wet-skid performance without deteriorating rolling resistance and abrasion resistance. This rubber composition, however, still has room for improvement in terms of achieving a balanced improvement in these properties.